The present invention relates to a method of controlling access to an area accessible by persons, particularly to a space closed by a door. For carrying out the method at least two communications units for transmitting and receiving an identification code, an acknowledgement code and an access code are provided. In the method the identification code is transmitted from a first communications unit to at least one second communications unit. The second communications unit checks the identification code and transmits the acknowledgement code back to the first communications unit if the check was successful. The first communications unit then transmits the access code to the second communications unit. After a successful check of the access code the access is freed.
Modern access control systems for buildings are frequently served by a chipcard on which an electronic key is filed. In order, for example, to grant access to an elevator installation a terminal with a reader for checking the chipcard and delivering a destination call is arranged on each floor in the vicinity of the elevator. Chipcards of that kind can also be integrated or inserted into a mobile communications equipment, such as, for example, a mobile telephone. However, in the case of access control systems of that kind there is the disadvantage that the mobile communications unit, from which the destination call is delivered, cannot be precisely localized in terms of position. In particular, it is frequently not possible to identify at which floor the destination call has been placed. As a consequence thereof, the destination call control of the elevator installation does not have information with regard to the floor at which the passenger to be transported is located.
A system for guiding a user in a building is known from European patent application EP 1 329 409 A2. This access control system comprises at least one transmitter/receiver unit for communication with a communications means of the user as well as at least one computer equipment for providing items of information for the user. The transmitter/receiver unit serves the purpose of identifying the communications means of the user locally within the building. The computer equipment communicates, by way of the transmitter/receiver unit, data for guidance of the user in the building to the communications means.
In this access control system it has proved disadvantageous that for localization of the communications means several transmitter/receiver units simultaneously transmit code sequences for localization of the communications means, whereby superimposition of the code sequences can occur. Beyond that, localization of the user is made difficult in that the identification code transmitted by the communications means reaches several transmitter/receiver units. Even in the case of two transmitter/receiver units, which for example are arranged on two different floors, receiving the identification code the computer unit cannot distinguish whether the communications means and thus the user is located in the vicinity of one transmitter/receiver unit on the other transmitter/receiver unit.